Method of producing an aluminum alloy



United States Patent 3 157 494 Mnrrron or PRonUciNo AN ALUMINUM ALLOY William B. Larson, Saginaw, Mich, assignor to General Motors Corporation, Detroit, Micla, a corporation of Delaware No Drawing. Filed Feb. 12, 1962, Ser. No. 172,763 7 Claims. (Cl. 75-134) This invention relates to a process for producing a fine-grained aluminum casting alloy and to a silicon base prealloy used in this process.

Frequently it is desirable to produce aluminum base casting alloys having fine grain structures. Additions of small amounts of boron and titanium to such alloys have been found to reduce the grain size. While these alloying elements may be added as minor constituents in an aluminum base master alloy, such master alloys are relatively expensive because of the difficulties involved in producing a homogeneous aluminum prealloy containing the high melting point constituents.

A principal object of the present invention, therefore is to provide a process in which desired small amounts of titanium and boron are introduced into an aluminum alloy in an inexpensive manner to produce a casting alloy having the desired fine grain structure. A further object of the invention is to provide a silicon base prealloy which can be used to prepare a fine-grained aluminum alloy at reduced cost as compared with processes employed previously. Adding boron and titanium to aluminum by means of the silicon prealloy is considerably less expensive than adding these constituents in the form of an aluminum base prealloy because the boron may be introduced into the silicon during preparation of the latter without any measurable cost premium, while the inclusion of titanium in the silicon involves only a very slight additional expense. Moreover, the use of silicon base prealloy containing titanium and/or boron is a much more desirable means of introducing these latter elements since a greater quantity of silicon-titanium-boron alloy can be added to the aluminum melt as compared with an aluminum-titanium-boron alloy. Consequently a more homogeneous solutioning of the boron and titanium is obtained.

These and other objects are attained in accordance with this invention by a process in which a silicon base prealloy containing approximately 0.06% to 0.3% by weight of boron and/or 0.3% to 1.5% by weight of titanium is added to aluminum to produce an aluminum casting alloy having a fine grain structure. In general, it is preferable to use both boron and titanium and to maintain the ratio of the titanium to the boron between about 4 to 1 and 6 to l. The same ratio normally is retained in the final aluminum base alloy.

The silicon may be prepared by first melting silica rock at a temperature of about 2600 F. to 3200 F. in a direct arc electric furnace under a reducing slag, such as one composed of approximately 85% limestone, 10% calcium carbide and fluorspar. After the silica is reduced, the slag is skimmed from the surface of the melt. The silicon formed in this manner is next tapped into a ladle and the boron and titanium added to the molten silicon to produce a silicon base prealloy having the aforementioned desirable composition. The contents of the ladle then may be poured into large pans and permitted to solidify.

Pure aluminum is melted in any suitable gas-fired or electric furnace at a temperature of about 1250 F. to

to include magnesium in the aluminum alloy composition, and this element may be introduced into the aluminum base alloy melt at the same time as the silicon. After the alloying constituents have completely dissolved in the aluminum, the melt preferably is fluxed with a reduring gas, such as Al Cl or chlorine gas, to remove oxides and any occluded gases. The resultant molten aluminum base alloy next is successively poured into a ladle and into suitable molds.

An example of an aluminum base casting alloy which has a combination of fine grain structure and desirable mechanical properties is an alloy consisting essentially of about 92% aluminum, 7% silicon, 0.004% boron, 0.02% titanium, 0.4% magnesium, iron not in excess of 0.5% and copper not in excess of 0.2%. Generally, an alloy of this type may have a silicon content ranging between about 6.5% and 7.5%, a boron content between 0.004% and 0.02% and 0.02% to 0.1% titanium. The balance of 91.2% to 93.2% is aluminum except for small amounts of iron, copper and other impurities. This aluminum base casting alloy can be produced conveniently and relatively inexpensvely by using a silicon base prealloy which constitutes approximately 7% by weight of the final aluminum alloy and which consists essentially of about 0.06% boron, 0.3% titanium and the balance substantially all silicon.

While my invention has been described by means of certain specific examples, it is to be understood that its scope is not to be limited thereby except as defined in the following claims.

I claim:

1. A method of producing a fine grain structure in a cast aluminum alloy, said method comprising melting together aluminum and a silicon base prealloy consisting essentially of about 0.06% to 0.3% boron, 0.3% to 1.5% titanium and the balance substantially all silicon, fluxing said melt, and thereafter pouring the resultant aluminum base alloy into a mold.

2. A method of producing an aluminum casting alloy having a fine grain structure which comprises melting together aluminum and a prealloy consisting essentially of at least one element selected from the group consisting of boron and titanium in amounts of approximately 0.06% to 0.3% and 0.3% to 1.5%, respectively, and the balance substantially all silicon, fluxing said melt and thereafter casting the resultant aluminum base alloy into a mold.

3. A method of producing an aluminum casting alloy having a fine grain structure, said method comprising melting together aluminum and a silicon base prealloy consisting essentially of about 0.06% to 0.3% boron, 0.3% to 1.5 titanium and the balance substantially all silicon, the ratio of the titanium to boron in said prealloy being between 4 to l and 6 to 1, fluxing said melt with a reducing gas and thereafter casting the resultant aluminum base alloy into a mold.

4. A method of producing an aluminum casting alloy having a fine grain structure, said method comprising melting together aluminum, magnesium and a silicon base prealloy consisting essentially of about 0.06% to 0.3% boron, 0.3% to 1.5% titanium and the balance silicon to form an aluminum base alloy comprising approximately 6.5% to 7.5% silicon, 0.004% to 0.02% boron, 0.02% to 0.1% titanium, 0.3% to 0.5% magnesium, O to 0.5 iron, 0 to 0.2% copper and the balance substantially all aluminum, the ratio of the titanium to boron in said aluminum base alloy being between 4 to 1 and 6 to l, fluxing said melt and thereafter casting the resultant aluminum base alloy into a mold.

5. A silicon base prealloy for addition to aluminum to produce an aluminum base casting alloy having a fine grain structure, said silicon base prealloy consisting 03% to 1.5% titanium, the ratio of the titanium to boron in said prealloy being between 4 to 1 and, 6 to 1.

' 71A method of producing 'an aluminum casting alloy having a fine grain structure,'said method comprising,

melting together aluminum and a silicon base prealloy con-sisting'essentially of about 0.06% to; 0.3% boron,

053% to 1.5% titanium and'the balance substantially all silicon to form an aluminum base alloy comprising ap- 4 proximately 6.5% to 7.5% silicon, 0.004% to 0.02% boron, 0.02% to 0.1% titanium :-and the balancesubstantially all aluminum, and thereafter casting the resultant. 7

aluminum base alloy into a mold.

References Qited in thefile of this patent UNITED STATES PATENTS 2,280,063 Critchett et a1, Apr. 21, 1942 2,280,283 Crafts Apr. 21, 1942 2,469,418 Striplin May 10, 1949 2,841,512 Cooper July 1, 1958 2,908,566

Cron etal Oct. 13, 1959 

5. A SILICON BAS PREALLOY FOR ADDITION TO ALUMINUM TO PRODUCE AN ALUMINUM BASE CASTING ALLOY HAVING A FINE GRAIN STRUCTURE, SAID SILICON BASE PREALLOY CONSISTING ESSENTIALLY OF ABOUT 0.06% TO 0.3% BORON, 0.3% TO 1.5% TITANIUM AND THE BALANCE SUBSTANTIALLY ALL SILICON. 